1. Field of the Invention
The invention relates to a wood adhesive and a method of preparing thereof.
2. Description of the Related Art
There are many types of wood adhesives currently known, among which urea-formaldehyde resin adhesive, phenolic resin adhesive, and melamine formaldehyde resin adhesive are dominant. However, upon production and application of plywood including these wood adhesives, formaldehyde, which is poisonous, will be released. The release period of formaldehyde is up to between 3 and 15 years.
For a newly-decorated house, formaldehyde cannot be evaporated completely within between 1 and 2 years, which results in a long-term high content of formaldehyde indoors and does harm to human health. Properties of urea-formaldehyde resin adhesive result in the inevitable release of free formaldehyde upon production of plywood. To reduce the content of formaldehyde in adhesives simply means weakening the bonding strength. Thus, in order to make the release of formaldehyde meet the E2, E1 or even E0 standard, many plywood producers passively deal with formaldehyde by masking, absorption, or blocking. Once the condition is mature, there is still a large amount of formaldehyde released. Although there are some formaldehyde-free wood adhesives, their hot water resistance is poor.